This invention concerns a valve or stopcock which can be adjusted to selectively control the flow of fluid from two or more fluid sources. Generally, valves of this type comprise a valve body into which is fitted a rotatable plug. Arms or conduits extend outwardly from the valve body and can be placed in communication with fluid sources. Slots or passageways in the plug are registrable with any two or more of the conduits at any one time to thereby control fluid flow through these conduits. The plug passageways can also be rotated to a position to prevent all fluid flow through the valve body conduits.
Valves of this nature have found many hospital and medical uses. A typical use, for example, is where one of the valve conduits goes, via appropriate tubing directly to a patient's bloodstream. Another conduit is connected to a parenteral solution and a third conduit may be connected to a syringe, a manometer, a second solution, medication, blood or plasma. Such an arrangement is commonly used during surgery, preoperative care, post-operative care, and in other patient care situations requiring infusion of fluids intravenously. Frequently, the patient is continuously infused with a parenteral solution. Thus, the valve plug is rotated to a position where the parenteral solution conduit is in communication with the conduit leading to the patient. During surgery and other patient care situations it is sometimes desirable to inject into the patient a medication such as, in addition to the parenteral solution, an anesthetic or muscle relaxer. To accomplish such an injection with this type of valve, the plug is rotated in the valve body to either cut off the flow of parenteral solution while the medication is injected or to simultaneously inject the medication and the parenteral solution. Once the medication had been completely administered, the valve plug was again rotated to a position where only the parenteral solution is in communication with the patient's bloodstream.
Problems which have been experienced with such valves include cracking of the valve body, cracking of the plug, separation of the plug from the valve body, leakage of fluid at the interface of the plug and valve body, and leakage between conduits when the valve is in a closed position. Such problems can be caused by inadequacies in the design, inadequacies of the valve materials used, and/or inadequate control of material processing methods or storage.
Prior art valves utilizing thermoplastics for construction generally comprises a plug having a diameter greater than the valve body socket with which it is mated. The larger diameter plug creates an interference fit between the plug and valve body socket and is intended to prevent undesirable leakage of fluids.
The interference fit results in compressive forces acting on the plug and tensile forces acting on the valve body. If such forces are great enough, cracking of the plug and/or valve body can occur, or the plug can be expelled from the valve body. The latter can occur if inadequate means are employed to retain the plug in the valve body, and is more apt to occur as a result of high internal pressures generated during infusion of fluids.
Cracking has been found to occur during assembly of the plug and body, at various times after assembly, and during use. Such cracking may be caused by a dimensional or physical change in the materials used, due to normal aging, exposure to high or low temperatures, exposure to radiation, or exposure to atmospheric pollutants.
To overcome cracking problems, one of the valve members (generally the plug) is made of a softer or more resilient material than the other, with the design such as to maintain compressive and tensile forces within acceptable limits.
Leakage which occurs at low pressures (below specified limits) can make such valves unacceptable for use. Such leakage may be caused by imperfections on the mating surfaces of the plug and/or valve body socket, a design deficiency which does not permit an adequate fit between the plug and valve body in the conduit area, cold flow (creep) of the plug away from the mating valve body surface in the conduit area, expansion or contraction of one member with temperature changes causing a separation of the mating surfaces in the conduit area, or a lifting of the plug in the valve body with internal pressure generated during infusion which again causes a separation of the mating surfaces in the conduit area.
Means for holding the plug in the body of prior art valves have been of a permanent or static nature. For example, a number of prior art valves have a plug which carries a flange which snaps over and under another flange on the periphery of the valve body. These interlocking flanges permanently hold the plug in the valve body and prevent it from popping out of the valve body under extreme pressure. However, since these valves do not allow for any plug movement, the plug or valve body may crack or break.
Other valves which have some space between the top of the plug and the valve body will allow the plug to move upwardly in the valve body. However, there is no structure in these valves to urge the plug back down into the valve body socket when the pressure decreases.
Some prior art valves are described in U.S. Pat. Nos. 2,832,562; 2,854,027; 2,859,932; 3,012,752; 3,048,192; 3,057,350; 3,276,472 and 3,481,367.